The generation of hydrogen from natural gas via steam reforming is a well established commercial process. One drawback is that commercial units tend to be extremely large in volume and subject to significant amounts of methane slip, identified as methane feedstock which passes through the reformer un-reacted.
To reduce the size and increase conversion efficiency of the units, a process has been developed which uses calcium oxide to improve hydrogen yield by removing carbon dioxide generated in the reforming process. See U.S. patent application Ser. No. 10/271,406 entitled “HYDROGEN GENERATION APPARATUS AND METHOD”, filed Oct. 15, 2002, commonly owned by the assignee of the present invention, the disclosure of which is incorporated herein by reference. The calcium oxide reacts with the CO2 in a separation reaction, producing a solid calcium carbonate (CaCO3) and absorbing the CO2.
Limitations on the calcium carbonate reuse process include that as the calcium carbonate, in either CaCO3 or CaO (solid) forms are circulated, both pumping and metering are required at the inlets to the hydrogen generator and a calcination reactor (where the CO2 is removed). Accurate metering of this high temperature granular material while pumping it into higher pressure regions has commonly been performed using very tall stand pipes and riser systems (such as developed by KBR Inc. of Houston, Tex.). These stand pipe transfer systems are large, some exceeding 15.24 m (50 ft) in height, and do not provide for downstream solids flow splitting required for the calcination reactor. With the large size of these units, gas leakage from or into the system is also an issue.